This application is directed to orthodontic appliances in general, and more particularly, to devices for applying external tension to extra-oral orthodontic devices.
Extra-oral orthodontic devices are normally of the type in which the teeth are placed in traction through the use of a tensioning means connected to a neck band or to a head band which is normally worn on the patient's neck or head. Traction is applied to the teeth through an outer face bow and tensioning means usually include two hooks, one on each side of the mouth. The hooks extend back along the sides of the face and are secured to the neck band or head band by the tensioning means. If the neck band extends around the back of the neck from ear to ear, it is generally referred to as a cervical strap. If the head band extends around the back of the head from ear to ear, it is usually referred to as an occupital strap. In the past, the tensioning device used to connect the hooks to the neck band or head band has commonly been an elastic or other resilient band arrangement capable of continuously biasing the outer face bow.
Types of prior art resilient neck or head bands are shown for example in U.S. Pat. Nos. 2,874,468, 3,765,093, 3,512,257 and 3,186,089. The prior art resilient neck band constructions have been used essentially for tensioning the orthodontic appliances and continuously act to pull the inside bow rearwardly in the mouth of the patient.
Recently, it has been found that the very tensioning means which acts to pull the inside bow rearwardly in the mouth of the patient presents a considerable hazard when mischievious or negligent persons unthinkingly act to pull the face bow forwardly in the mouth of the patient. In fact, there is at least one reported occurrence wherein the face bow was pulled forwardly against the bias of the neck band and then released to cause a portion of the inside bow to pierce the eye of the patient thereby causing grevious injury.